class Solution {
public:
    void reverseString(vector<char>& s) 
    {
        int i = 0;
        int j = s.size() - 1;
        char tmp;

        while(i < j)
        {
            tmp = s[i];
            s[i] = s[j];
            s[j] = tmp;

            i++;
            j--;
        }
    }
};